The present invention relates to headlamps for power vehicles.
Headlamps for power vehicles are known in the art in various modifications. One of such headlamps is disclosed for example in the German document DE-OS 1,497,355. This headlamp has a parabolic reflector, and an incandescent lamp with a single incandescent coil inserted in the reflector. Moreover, a shield is provided which partially surrounds the periphery of the incandescent lamp and is movable relative to the incandescent lamp in the optical axis of the reflector. The incandescent lamp is also movable along the optical axis. In the position of low beam the incandescent coil is withdrawn from the focus of the reflector and the shield to a position in which it blocks the light from the light source to an upwardly reflecting region of the reflector. In the position for low beam the incandescent coil is arranged in the region of the focus of the reflector and the shield can reach the position in which the light from the light source is on the whole reflector. Movement of the incandescent coil from the focus of the reflector is necessary to obtain an inclination of the light relative to the roadway, required for the low beam. The switching from the high beam to the low beam and vice versa requires therefore high expenses since the incandescent lamp and the shield must be adjusted. With the parabolic reflector, moreover, neither a favorable light distribution for the low beam nor a favorable light distribution for the high beam is produced.
For simplifying the switching from the high beam to the low beam, also incandescent lamps with two incandescent coils are known. One incandescent coil serves for the low beam and the other incandescent coil serves for the high beam.
Gas-discharge lamps provided for new headlamps have a discharge spark which requires a longer starting time until it reaches the maximum right intensity, as compared with the incandescent lamps. The system in the low beam and high beam are possible only by alternating operation of the two light arcs, since here a dark phase is produced until the other light arc reaches its highest light intensity.